Evolution of life forms and mycorrhizal relationships in Cymbidium

兰花属(Cmbidium Sw.)，为兰科植物。东亚和东南亚至澳大利亚，由约50种组成。该属表现出独特的生态多样性，出现在陆地、附生和岩生生命形式中。此外，大花组植物缺乏叶片，具有专性的真菌营养存在。本研究对兰属及其姊妹群的各种形态解剖特征与生态特征之间的相关性进行了研究。此外，利用兰属(Yukawa et al.2002)的分子系统树分析了这些性状的系统发育限制。主要研究结果如下：(1)在兰属植物中，岩生和陆生生物可能至少三次起源于附生生境。(2)专性菌根谱系--大花组地衣与陆生祖细胞分化而来。(3)附生植物种子表现出较高的…比陆生物种更搞笑，维度更大。(4)专性真菌营养种的种子大小明显小于其光合作用的姊妹种。(5)分枝根状茎的发育仅见于陆生物种。我们发现这种类型的根茎是菌根真菌的主要栖息地。(6)在该属植物中，厚壁组织纤维的发育与附生程度有关。(7)栅栏组织的分化和两栖动物可能适应强光胁迫，因为具有这些特征的物种栖息在裸露部位的树木上。(8)在兰花的根和/或根茎中发现兰型菌根真菌和树种外生菌根真菌。虽然陆生大花兰与这两种真菌共生，但附生植物只与兰科内生菌根真菌共生。另一方面，专性真菌营养物种仅与树木外生菌根真菌共生。较少

Cymbidium Sw., an orchid genus distributed from. East and Southeast Asia to Australia, comprises about 50 species. The genus exhibits distinctive ecological diversification and occurs in terrestrial, epiphytic, and lithophytic life forms. Moreover, Cymbidium section Pachirhizanthe lacks foliage leaves and has an obligate mycotrophic nutritional existence. In this study correlation between various morphological and anatomical characters and ecological characters was tested for most species of Cymbidium and its sister groups. Furthermore, a molecular phylogenetic tree of Cymbidium (Yukawa et al.2002) was used to examine phylogenetic constraint of these characters. The following insights were provided : (1)In Cymbidium, lithophytic and terrestrial life forms were likely to be derived from epiphytic habitat at least three times. (2)The obligate mycotrophic lineage, Cymbidium section Pachyrhizanthe diverged from a terrestrial progenitor. (3)The seed of epiphytic species showed higher hydrop … More hilicity and larger dimensions than that of terrestrial species. (4)The seed size of obligate mycotrophic species decreased greatly in comparison with its sister photosynthetic species. (5)Development of ramified rhizomes was found only in terrestrial species. We found that this type of the rhizome is the principal dwelling for mycorrhizal fungi. (6)In this genus, development of sclerenchymatous fibers in leaves is correlated to the degree of epiphytism. (7)Differentiation of palisade tissue and amphistomaty are likely adapted to high light stress because the species possessing these characters inhabit trees at exposed positions. (8)Orchid-type endomycorrhizal fungi and tree ectomycorrhizal fungi were found in Cymbidium roots and/or rhizomes. Although terrestrial Cymbidium species symbiose with both types of fungi, epiphytic species show symbiosis only with Orchid-type endomycorrhizal fungi. On the other hand, obligate mycotrophic species symbiose exclusively with tree ectomycorrhizal fungi. Less